Kinetics of inactivation of Bacillus spores using low temperature argon plasma at different microwave power densities

The objective of this study was to determine the remarkable role of the microwave power density of argon plasma in the inactivation of Bacillus subtilis, Bacillus stearothermophilus and Bacillus pumilus spores deposited on polypropylene bio-indicator carriers. In particular, spore survival by argon plasma was determined as a function of the initial spore density of the bio-indicators. The microwave induced argon plasmas were generated at 1.47, 2.63 and 4.21 w/cm³ microwave power densities under a low gas pressure of 50 Pa at an ambient temperature of 15 °C to reach low temperature distribution of 31, 35 and 43 °C, respectively. Our results indicate that the different Bacillus spores showed distinct degrees of argon plasma sensitivity, and spore survival was significantly reduced when the microwave power density of the plasma treatments was increased. Among the three Bacillus strains, Bacillus subtilis was the most argon plasma resistant, whereas Bacillus stearothermophilus was the most sensitive. However, spore survival was not affected by the initial spore density of the bio-indicators. Only a certain degree of the spore inactivation log (N_o/N) from 1.67 to 1.95 was observed despite the 4-order differences in the initial spore density of the Bacillus pumilus bio-indicators.